13. Food Webs and Community Structure

Cohen, Joel E.

doi:10.1515/9781400860180.181

Cited by 56 publications

(63 citation statements)

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“…It also implies that a given species essentially does not eat other species that are larger than itself, which suggests a body-size-based hierarchy. Body size has been suggested previously to provide a mechanistic interpretation for the hierarchy assumption in the cascade model (Cohen and Newman 1985), both by Warren and Lawton (1987) and by Cohen (1989). However, in our analysis we did not postulate a size hierarchy as such: instead, this hierarchy naturally emerges from the scaling relations and size-dependent functional response suggested by DEB theory, and in particular from the considered proportionality of capture time to predator-prey size ratio.…”

Section: Imperfect Upper Triangularitymentioning

confidence: 52%

Joint evolution of predator body size and prey-size preference

2007

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We studied the joint evolution of predator body size and prey-size preference based on dynamic energy budget theory. The predators' demography and their functional response are based on general eco-physiological principles involving the size of both predator and prey. While our model can account for qualitatively different predator types by adjusting parameter values, we mainly focused on 'true' predators that kill their prey. The resulting model explains various empirical observations, such as the triangular distribution of predator-prey size combinations, the island rule, and the difference in predator-prey size ratios between filter feeders and raptorial feeders. The model also reveals key factors for the evolution of predator-prey size ratios. Capture mechanisms turned out to have a large effect on this ratio, while prey-size availability and competition for resources only help explain variation in predator size, not variation in predator-prey size ratio. Predation among predators is identified as an important factor for deviations from the optimal predator-prey size ratio.

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Section: Imperfect Upper Triangularitymentioning

confidence: 52%

Joint evolution of predator body size and prey-size preference

2007

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“…Be this as it may, the next, Keplerian, phase is to seek patterns in these webs (Cohen 1989(Cohen , 1994Cohen et al 1990;Pimm 1982;Sugihara et al 1989). One interesting, though controversial, suggestion is of`link^species scaling invariance' (LSSI).…”

Section: Food Web Patternsmentioning

confidence: 99%

Unanswered questions in ecology

May

1999

Phil. Trans. R. Soc. Lond. B

157

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This is very much a personal view of what I think are some of the most important unanswered questions in ecology. That is, these are the questions that I expect will be high on the research agenda over the coming century. The list is organized hierarchically, beginning with questions at the level of individual populations, and progressing through interacting populations to entire communities or ecosystems. I will try to guess both at possible advances in basic knowledge and at potential applications. The only thing that is certain about this view of the future is that much of it will surely turn out to be wrong, and many of the most interesting future developments will be quite unforeseen.

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“…The food web attributes measured were number of species (n); top (T), intermediate (I), and basal (B) trophic fractions (Cohen 1989a C p L/n fraction of cycles, which are trophic relationships of the form "A eats B, B eats C, … eats A," excluding cannibalism ("A eats A") and mutual predation ("A eats B, B eats A"; Cattin et al 2004); short-weighted trophic level (Levine 1980;Williams and Martinez 2004); omnivory degree (Williams and Martinez 2000); generality (G) and vulnerability (V; Schoener 1989); normalized standard deviations of generality (SD(G)) and vulnerability (SD(V); Williams and Martinez 2000); and motifs and antimotifs (Milo et al 2002). A detailed description of these measures can be found in "Detailed Description of Food Web Attributes" in the online edition of the American Naturalist.…”

Section: Measuring Food Web Attributesmentioning

confidence: 99%

“…While no documented food web is a perfect representation, these webs are the product of 20 years of generalizations about food web structure and critiques of the same. Many have been collated specifically to address the criticisms leveled at earlier webs (Briand andCohen 1984, 1987;Cohen 1989a), such as incompleteness (Hall andRaffaelli 1991, 1993;Goldwasser and Roughgarden 1997), the practice of lumping species together (Lawton and Warren 1988;Paine 1988;Pimm and Kitching 1988;Sugihara et al 1989;Warren 1989;Hall and Raffaelli 1991;Pimm et al 1991;Martinez 1993;Martinez et al 1999), and taxonomic bias (May 1983;Paine 1988;Sugihara et al 1997). Therefore, these webs represent the best information that is available to us about food web structure.…”

mentioning

confidence: 99%

“…Starting with the cascade model (Cohen and Newman 1985), these models have shown how simple heuristics governing the trophic interactions between individual species can predict whole-web structure. The cascade model assumed that there was a one-dimensional niche ordering, such as body size (Cohen 1989b), which meant that no species could prey on another species with a niche value higher than its own. The niche model built on this by introducing a contiguous feeding range and relaxing the feeding hierarchy of the cascade model (Williams and Martinez 2000).…”

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confidence: 99%

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Permanence Does Not Predict the Commonly Measured Food Web Structural Attributes

Kristensen¹

2008

The American Naturalist

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Submitted April 9, 2007; Accepted September 13, 2007; Electronically published December 14, 2007 Online enhancement: appendix.abstract: Food web assembly algorithms show great promise for investigating issues involving the dynamics of whole webs, such as succession, rehabilitation, and invasibility. Permanence, which requires that all species densities remain positive and finite, has been suggested as a good stability constraint. This study tests the validity of the permanence constraint by comparing real webs and model webs from the literature to the predictions of three assembly algorithms: one constrained by permanence and feasibility, one constrained by feasibility alone, and one with no dynamical constraint. It is found that the addition of the permanence constraint does not improve the predictive ability of the algorithm. Its main effect is to increase the efficiency of species selected for the web. Dynamically constrained webs have lower connectance and indistinct trophic levels compared to real webs and webs from other models, which is a consequence of omitting species' physiology. Although webs are less likely to be permanent if they have high omnivory and cycling, the web-building process circumvents this constraint. The challenges of testing and justifying system-level hypotheses, including isolating and detecting their effects, are discussed.Keywords: food webs, stability, permanence, feasibility, niche model, nested-hierarchy model.A food web-building algorithm is a series of repeating steps by which model food webs can be created. Starting with one or a few species, the algorithm permits new species to invade and some species to be lost at each time Weatherby et al. 1998;Chase 2003;Fukami 2004). Because assembly algorithms simulate invasion and extinction in a whole food web, they hold great promise for answering questions about succession, rehabilitation, and invasibility. The rules governing which food webs survive intact to the next time step are often based on dynamical constraints (though not always; e.g., Luh and Pimm 1993). For example, food webs may be constrained to be feasible (i.e., all species have a positive steady state biomass [e.g., Tregonning and Roberts 1979]) or locally stable (e.g., Post and Pimm 1983). This article focuses on a dynamical constraint called permanence. A food web is permanent if the densities of all species remain positive and finite and it can recover after those densities are brought arbitrarily close to 0 (Hofbauer and Sigmund 1988). Permanence has the advantage over local stability in that it does not presuppose the existence of a single steady state but does allow for complex trajectories within the phase space, such a...

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13. Food Webs and Community Structure

Cited by 56 publications

References 0 publications

Joint evolution of predator body size and prey-size preference

Joint evolution of predator body size and prey-size preference

Unanswered questions in ecology

Permanence Does Not Predict the Commonly Measured Food Web Structural Attributes

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